Cyclosporines are members of a class of cyclic polypeptides having potent immunosuppressant activity. At least some of these compounds, such as Cyclosporine A (CsA), are produced by the species Tolypocladium inflatum as secondary metabolites. CsA is a potent immunosuppressive agent that has been demonstrated to suppress humoral immunity and cell-mediated immune reactions, such as allograft rejection, delayed hypersensitivity, experimental allergic encephalomyelitis, Freund's adjuvant arthritis and graft versus host disease. It is used for the prophylaxis of organ rejection in organ transplants; for the treatment of rheumatoid arthritis; and for the treatment of psoriasis.
Although a number of compounds in the cyclosporine family are known, CsA is perhaps the most widely used medically. The immunosuppressive effects of CsA are related to the inhibition of T-cell mediated activation events. Immunosuppression is accomplished by the binding of cyclosporine to a ubiquitous intracellular protein called cyclophilin (CyP). This complex, in turn, inhibits the calcium and calmodulin-dependent serine-threonine phosphatase activity of the enzyme calcineurin. Inhibition of calcineurin prevents the activation of transcription factors, such as NFATp/c and NF-κB, which are necessary for the induction of cytokine genes (IL-2, IFN-γ, IL-4, and GM-CSF) during T-cell activation.
Since the original discovery of cyclosporine, a wide variety of naturally occurring cyclosporines have been isolated and identified. Additionally, many cyclosporines that do not occur naturally have been prepared by partial or total synthetic means, and by the application of modified cell culture techniques. Thus, the class comprising cyclosporines is substantial and includes, for example, the naturally occurring cyclosporines A through Z; various non-naturally occurring cyclosporine derivatives; artificial or synthetic cyclosporines including the dihydro- and iso-cyclosporines; derivatized cyclosporines (for example, either the 3′-O-atom of the MeBmt residue may be acylated, or a further substituent may be introduced at the sarcosyl residue at the 3-position); cyclosporines in which the MeBmt residue is present in isomeric form (e.g., in which the configuration across positions 6′ and 7′ of the MeBmt residue is cis rather than trans); and cyclosporines wherein variant amino acids are incorporated at specific positions within the peptide sequence.
Cyclosporine analogues containing modified amino acids in the 1-position are disclosed in WO 99/18120 and WO 03/033527, which are incorporated herein by reference in their entirety. These applications describe a cyclosporine derivative known as “ISATX247” or “ISA247” or “ISA.” This analog is structurally identical to CsA, except for modification at the amino acid-1 residue. Applicants have previously discovered that certain mixtures of cis and trans isomers of ISA247, including mixtures that are predominantly comprised of trans ISA247, exhibited a combination of enhanced immunosuppressive potency and reduced toxicity over the naturally occurring and presently known cyclosporines.
Cyclosporine has three well established cellular targets; calcineurin, the CyP isoforms (which includes but is not limited to CyP-A, CyP-B and CyP-D), and P-glycoprotein (PgP). The binding of cyclosporine to calcineurin results in significant immunosuppression and is responsible for its traditional association with transplantation and autoimmune indications.
The Cyclophilin Family
CyPs (Enzyme Commission (EC) number 5.1.2.8) belong to a group of proteins that have peptidyl-prolyl cis-trans isomerase activity; such proteins are collectively known as immunophilins and also include the FK-506-binding proteins and the parvulins. CyPs are found in all cells of all organisms studied, in both prokaryotes and eukaryotes and are structurally conserved throughout evolution. There are 7 major CyPs in humans, namely CyP-A, CyP-B, CyP-C, CyP-D, CyP-E, CyP-40, and CyP-NK (first identified from human natural killer cells), and a total of 16 unique proteins (Galat A. Peptidylprolyl cis/trans isomerases (immunophilins): biological diversity—targets—functions. Curr Top Med Chem 2003, 3:1315-1347; Waldmeier P C et al. Cyclophilin D as a drug target. Curr Med Chem 2003, 10:1485-1506).
The first member of the CyPs to be identified in mammals was CyP-A. CyP-A is an 18-kDa cytosolic protein and is the most abundant protein for CsA binding. It is estimated that CyP-A makes up 0.6% of the total cytosolic protein (Mikol V et al. X-ray structure of monmeric cyclophilin A-cycloporin A crystal complex at 2.1 A resolution. J. Mol. Biol. 1993, 234:1119-1130; Galat A, Metcalfe S M. Peptidylproline cis/trans isomerases. Prog. Biophys. Mol. Biol. 1995, 63:67-118).
Cellular Location of Cyclophilins
CyPs can be found in most cellular compartments of most tissues and encode unique functions. In mammals, CyP-A and CyP-40 are cytosolic whereas CyP-B and CyP-C have amino-terminal signal sequences that target them to the endoplasmic reticulum protein secretory pathway (reviewed in Galat, 2003; Dornan J et al. Structures of immunophilins and their ligand complexes. Curr Top Med Chem 2003, 3:1392-1409). CyP-D has a signal sequence that directs it to the mitochondria (Andreeva L et al. Cyclophilins and their possible role in the stress response. Int J Exp Pathol 1999, 80:305-315; Hamilton G S et al. Immunophilins: beyond immunosuppression. J Med Chem 1998, 41:5119-5143); CyP-E has an amino-terminal RNA-binding domain and is localized in the nucleus (Mi H et al. A nuclear RNA-binding cyclophilin in human T cells. FEBS Lett 1996, 398:201-205) and CyP-40 has TPRs and is located in the cytosol (Kieffer L J et al. Cyclophilin-40, a protein with homology to the P59 component of the steroid receptor complex. Cloning of the cDNA and further characterization. J Biol Chem 1993, 268:12303-12310). Human CyP-NK is the largest CyP, with a large, hydrophilic and positively charged carboxyl terminus, and is located in the cytosol (Anderson S K et al. A cyclophilin-related protein involved in the function of natural killer cells. Proc Natl Acad Sci USA 1993, 90:542-546; Rinfret A et al. The N-terminal cyclophilin-homologous domain of a 150-kilodalton tumor recognition molecule exhibits both peptidylprolyl cis-transisomerase and chaperone activities. Biochemistry 1994, 33:1668-1673)
Function and Activity of the Cyclophilins
CyPs are multifunctional proteins that are involved in many cellular processes. Because CyPs were highly conserved throughout evolution, this suggests an essential role for CyPs. Initially, it was found that CyPs have the specific enzymatic property of catalyzing cis-trans isomerization of peptidyl-prolyl bonds (Galat, 1995; Fisher G A et al. A phase I study of paclitaxel (taxol) (T) in combination with SDZ valspodar, a potent modulator of multidrug resistance (MDR). Anticancer Drugs. 1994; 5(Suppl 1): 43). Thus, CyPs are called peptidyl-prolyl-cis-trans isomerase (PPlase), which can act as an acceleration factor in the proper folding of newly synthesized proteins, PPlases are also involved in repairing damaged proteins due to environmental stresses including thermal stress, ultraviolet irradiation, changes in the pH of the cell environment, and treatment with oxidants. This function is known as molecular chaperoning activity. (Yao Q et al. Roles of Cyclophilins in Cancers and Other Organs Systems. World J. Surg. 2005, 29: 276-280)
In addition, the PPlase activity of CyPs has recently been shown to be involved in diverse cellular processes, including intracellular protein trafficking (Andreeva, 1999; Caroni P et al. New member of the cyclophilin family associated with the secretory pathway. J Biol Chem 1991, 266:10739-42), mitochondrial function (Halestrap A P et al. CsA binding to mitochondrial cyclophilin inhibits the permeability transition pore and protects hearts from ischaemia/reperfusion injury. Mol Cell Biochem 1997, 174:167-72; Connern C P, Halestrap A P. Recruitment of mitochondrial cyclophilin to the mitochondrial inner membrane under conditions of oxidative stress that enhance the opening of a calcium-sensitive non-specific channel. Biochem J 1994, 302:321-4), pre-mRNA processing (Bourquin J P et al. A serine/argininerich nuclear matrix cyclophilin interacts with the Cterminal domain of RNA polymerase II. Nucleic Acids Res 1997, 25:2055-61), and maintenance of multiprotein complex stability (Andreeva, 1999).
Cyclosporine binds with nanomolar affinity to CyP-A via contacts within the hydrophobic pocket (Colgan J et al. Cyclophilin A-Deficient Mice Are Resistant to Immunosuppression by Cyclosporine. The Journal of Immunology 2005, 174: 6030-6038, Mikol, 1993) and inhibits PPlase activity. However, this effect is thought to be irrelevant for the immunosuppression. Rather, the complex between CsA and CyP-A creates a composite surface that binds to and prevents calcineurin from regulating cytokine gene transcription (Friedman J et al. Two cytoplasmic candidates for immunophilin action are revealed by affinity for a new cyclophilin: one in the presence and one in the absence of CsA. Cell 1991, 66: 799-806; Liu J et al. Calcineurin is a common target of cyclophilin-CsA and FKBP-FK506 complexes. Cell 1991, 66: 807-815).
Homology of the Cyclophilins
CyP-A, the prototypical member of the family, is a highly conserved protein in mammalian cells (Handschumacher R E et al. Cyclophilin: a specific cytosolic binding protein for CsA. Science 1984, 226: 544-7). Sequence homology analysis of human CyP-A shows that it is highly homologous to human CyP-B, CyP-C, and CyP-D (Harding M W, Handschumacher R E, Speicher D W. Isolation and amino acid sequence of cyclophilin. J Biol Chem 1986,261:8547-55). The cyclosporine binding pocket of all CyPs is formed by a highly conserved region of approximately 109 amino acids. Of the known CyPs, CyP-D has the highest homology to CyP-A. In fact, in this region the sequence identity is 100% between CyP-A and CyP-D (Waldmeier 2003; Kristal B S et al. The Mitochondrial Permeability Transition as a Target for Neuroprotection. Journal of Bioenergetics and Biomembranes 2004, 36(4); 309-312). Therefore, CyP-A affinity is a very good predictor of CyP-D affinity, and visa versa (Hansson M J et al. The Nonimmunosuppressive Cyclosporine analogues NIM811 and UNIL025 Display Nanomolar Potencies on Permeability Transition in Brain-Derived Mitochondria. Journal of Bioenergetics and Biomembranes, 2004, 36(4): 407-413). This relationship has been repeatedly demonstrated empirically with Cyclosporine analogues (Hansson, 2004; Ptak Rg et al. Inhibition of Human Immunodeficiency Virus Type 1 Replication in Human Cells by Debio-025, a Novel Cyclophilin Binding Agent. Antimicrobial Agents and Chemotherapy 2008: 1302-1317; Millay D P et al. Genetic and pharmacologic inhibition of mitochondrial dependent necrosis attenuates muscular dystrophy. Nature Medicine 2008, 14(4): 442-447; Harris R et al. The Discovery of Novel Non-Immunosuppressive Cyclosporine Ethers and Thioethers With Potent HCV Activity. Poster #1915, 59th Annual Meeting of the American Association for the Study of Liver Diseases (AASLD), 2008). The sequence homology across the CyPs suggests that all CyPs are potential targets for Cyclosporine analogues. Because of the multitude of cellular processes in which the CyPs are involved, this further suggests that CsA analogues that retain significant binding to CyP can be useful in the treatment of many disease indications.
Cyclophilin Mediated Diseases
Human Immunodeficiency Virus (HIV):
HIV is a lentivirus of the retrovirus family and serves as an example of the involvement of CyP in the process of infection and replication of certain viruses. CyP-A was established more than a decade ago to be a valid target in anti-HIV chemotherapy (Rosenwirth B A et al. Cyclophilin A as a novel target in anti-HIV-1 chemotherapy. Int. Antivir. News 1995, 3:62-63). CyP-A fulfills an essential function early in the HIV-1 replication cycle. It was found to bind specifically to the HIV-1 Gag polyprotein (Luban J K L et al. Human immunodeficiency virus type 1 Gag protein binds to cyclophilins A and B. Cell 1993, 73: 1067-1078). A defined amino acid sequence around G89 and P90 of capsid protein p24 (CA) was identified as the binding site for CyP-A (Bukovsky A A A et al. Transfer of the HIV-1 cyclophilin-binding site to simian immunodeficiency virus from Macaca mulatta can confer both cyclosporine sensitivity and cyclosporine dependence. Proc. Natl. Acad. Sci. USA 1997, 94: 10943-10948; Gamble T R F et al. Crystal structure of human cyclophilin A bound to the amino-terminal domain of HIV-1 capsid. Cell 1996, 87: 1285-1294). The affinity of CyP-A for CA promotes the incorporation of CyP-A into the virion particles during assembly (Thali M A et al. Functional association of cyclophilin A with HIV-1 virions. Nature 1994, 372: 363-365). Experimental evidence indicates that the CyP-A-CA interaction is essential for HIV-1 replication; inhibition of this interaction impairs HIV-1 replication in human cells (Hatziioannou T D et al. Cyclophilin interactions with incoming human immunodeficiency virus type 1 capsids with opposing effects on infectivity in human cells. J. Virol. 2005, 79: 176-183; Steinkasserer A R et al. Mode of action of SDZ NIM 811, a nonimmunosuppressive CsA analog with activity against human immunodeficiency virus type 1 (HIV-1): interference with early and late events in HIV-1 replication. J. Virol 1995, 69: 814-824). The step in the viral replication cycle where CyP-A is involved was demonstrated to be an event after penetration of the virus particle and before integration of the double-stranded viral DNA into the cellular genome (Braaten D E K et al. Cyclophilin A is required for an early step in the life cycle of human immunodeficiency virus type 1 before the initiation of reverse transcription. J. Virol 1996 70: 3551-3560; Mlynar E D et al. The non-immunosuppressive CsA analogue SDZ NIM 811 inhibits cyclophilin A incorporation into virions and virus replication in human immunodeficiency virus type 1-infected primary and growth-arrested T cells. J. Gen. Virol 1996, 78: 825-835; Steinkasserer, 1995). The anti-HIV-1 activity of CsA was first reported in 1988 (Wainberg M A et al. The effect of CsA on infection of susceptible cells by human immunodeficiency virus type 1. Blood 1998, 72: 1904-1910). Evaluation of CsA and many derivatives for inhibition of HIV-1 replication revealed that nonimmunosuppressive CsA analogs had anti-HIV-1 activities equal to or even superior to those of immunosuppressive analogs (Bartz S R E et al. Inhibition of human immunodeficiency virus replication by nonimmunosuppressive analogs of CsA. Proc. Natl. Acad. Sci. USA 1995, 92: 5381-5385; Billich A F et al. Mode of action of SDZ NIM 811, a nonimmunosuppressive CsA analog with activity against human immunodeficiency virus (HIV) type 1: interference with HIV protein-cyclophilin A interactions. J. Virol 1995, 69: 2451-2461; Ptak, 2008).
Inflammation
Inflammation in disease involves the influx of leukocytes (white blood cells) to the area of infection. The leukocytes are drawn to the area by chemokines, a family of chemoattracting agents. In vitro studies have shown that extracellular CyP-A is a potent chemoattractant for human leukocytes and T cells (Kamalpreet A et al. Extracellular cyclophilins contribute to the regulation of inflammatory responses Journal of Immunology 2005; 175: 517-522; Yurchenko V G et al. Active-site residues of cyclophilin A are crucial for its signaling activity via CD147. J. Biol. Chem. 2002; 277: 22959-22965; Xu Q M C et al. Leukocyte chemotactic activity of cyclophilin. J. Biol. Chem. 1992; 267: 11968-11971; Allain F C et al. Interaction with glycosaminoglycans is required for cyclophilin B to trigger integrin-mediated adhesion of peripheral blood T lymphocytes to extracellular matrix. Proc. Natl. Acad. Sci. USA 2002; 99: 2714-2719). Furthermore, CyP-A can induce a rapid inflammatory response, characterized by leukocyte influx, when injected in vivo (Sherry B N et al. Identification of cyclophilin as a proinflammatory secretory product of lipopolysaccharide-activated macrophages. Proc. Natl. Acad. Sci. USA 1992; 89: 3511-3515). CyP-A is ubiquitously distributed intracellularly, however, during the course of inflammatory responses, CyP-A is released into extracellular tissue spaces by both live and dying cells (Sherry, 1992). Indeed, elevated levels of CyP-A have been reported in several different inflammatory diseases, including sepsis, rheumatoid arthritis, and vascular smooth muscle cell disease (Jin Z G et al. Cyclophilin A is a secreted growth factor induced by oxidative stress. Circ. Res. 2000; 87: 789-796; Teger, 1997; Billich, 1997). In the case of rheumatoid arthritis, a direct correlation between levels of CyP-A and the number of neutrophils in the synovial fluid of rheumatoid arthritis patients was reported (Billich, 1997).
Cancer
CyP-A has recently been shown to be over-expressed in many cancer tissues and cell lines, including but not limited to small and non-small cell lung, bladder, hepatocellular, pancreatic and breast cancer (Li, 2006; Yang H et al. Cyclophilin A is upregulated in small cell lung cancer and activates ERK1/2 signal. Biochemical and Biophysical Research Communications 2007; 361: 763-767; Campa, 2003). In cases where exogenous CyP-A was supplied this was shown to stimulate the cancer cell growth (Li, 2006; Yang, 2007) while CsA arrested the growth (Campa, 2003). Most recently it has been demonstrated the CyP (A and B) is intricately involved in the biochemical pathway allowing growth of human breast cancer cells and that CyP knockdown experiments decreased the cancer cell growth, proliferation and motility (Fang F et al. The expression of Cyclophilin B is Associated with Malignant Progression and Regulation of Genes Implicated in the Pathogenesis of Breast Cancer. The American Journal of Pathology 2009; 174(1): 297-308; Zheng J et al. Prolyl Isomerase Cyclophilin A Regulation of Janus-Activated Kinase 2 and the Progression of Human Breast Cancer. Cancer Research 2008; 68 (19): 7769-7778). Most interestingly, CsA treatment of mice xenografted with breast cancer cells induced tumor necrosis and completely inhibited metastasis (Zheng, 2008). The researchers conclude that “Cyclophilin B action may significantly contribute to the pathogenesis of human breast cancer” and that “cyclophilin inhibition may be a novel therapeutic strategy in the treatment of human breast cancer” (Fang, 2009; Zheng, 2008).
Hepatitis C
Hepatitis C Virus (HCV) is the most prevalent liver disease in the world and is considered by the World Health Organization as an epidemic. Because HCV can infect a patient for decades before being discovered, it is often called the “silent” epidemic. Studies suggest that over 200 million people worldwide are infected with HCV, an overall incidence of around 3.3% of the world's population. In the US alone, nearly 4 million people are or have been infected with HCV and of these; 2.7 million have an ongoing chronic infection. All HCV infected individuals are at risk of developing serious life-threatening liver diseases. Current standard therapy for chronic hepatitis C consists of the combination of pegylated interferon in combination with ribavirin, both generalized anti-viral agents (Craxi A et al. Clinical trial results of peginterferons in combination with ribavirin. Semin Liver Dis 2003; 23(Suppl 1): 35-46). Failure rate for the treatment is approximately 50% (Molino B F. Strategic Research Institute: 3rd annual viral hepatitis in drug discovery and development world summit 2007. AMRI Technical Reports; 12(1)).
It has recently been demonstrated that CyP-B is critical for the efficient replication of the HCV genome (Watashi K et al. Cyclophilin B Is a Functional Regulator of Hepatitis C Virus RNA Polymerase. Molecular Cell 2005, 19: 111-122). Viruses depend on host-derived factors such as CyP-B for their efficient genome replication. CyP-B interacts with the HCV RNA polymerase NS5B to directly stimulate its RNA binding activity. Both the RNA interference (RNAi)-mediated reduction of endogenous CyP-B expression and the induced loss of NS5B binding to CyP-B decreases the levels of HCV replication. Thus, CyP-B functions as a stimulatory regulator of NS5B in HCV replication machinery. This regulation mechanism for viral replication identifies CyP-B as a target for antiviral therapeutic strategies.
Unlike other HCV treatments, CyP inhibition does not directly target the HCV virus. It is therefore thought that resistance to CyP binding drugs will occur more slowly than current HCV treatment drugs (Manns M P, et al. The way forward in HCV treatment-finding the right path. Nature Reviews Drug Discovery 2007; 6: 991-1000). In addition, by interfering at the level of host-viral interaction, CyP inhibition may open the way for a novel approach to anti-HCV treatment that could be complementary, not only to interferon-based treatment, but also to future treatments that directly target HCV replication enzymes such as protease and polymerase inhibitors (Flisiak R, Dumont J M, Crabbé R. Cyclophilin inhibitors in hepatitis C viral infection. Expert Opinion on Investigational Drugs 2007, 16(9): 1345-1354). Development of new anti-HCV drugs effecting HCV viral replication has been significantly impeded by the lack of a suitable laboratory HCV model. This obstacle has only recently been overcome by the development of several suitable cell culture models (Subgenomic HCV Replicon Systems) and a mouse model containing human liver cells (Goto K, et al. Evaluation of the anti-hepatitis C virus effects of cyclophilin inhibitors, CsA, and NIM811. Biochem Biophys Res Comm 2006; 343: 879-884; Mercer D F, et al. Hepatitis C virus replication in mice with chimeric human livers. Nat Med 2001; 7: 927-933). Cyclosporine has recently demonstrated anti-HCV activity in screening models and in small clinical trials (Watashi K, et al. CsA suppresses replication of hepatitis C virus genome in cultured hepatocytes. Hepatology 2003; 38:1282-1288; Inoue K, Yoshiba M. Interferon combined with cyclosporine treatment as an effective countermeasure against hepatitis C virus recurrence in liver transplant patients with end-stage hepatitis C virus related disease. Transplant Proc 2005; 37:1233-1234).
Muscular Degenerative Disorders
CyP-D is an integral part of the mitochondrial permeability transition pore (MTP) in all cells. The function of the MTP pore is to provide calcium homeostasis within the cell. Under normal conditions the opening and closing of the MTP pore is reversible. Under pathological conditions that involve an excessive calcium influx into the cell, this overloads the mitochondria and induces an irreversible opening of the MPT pore, leading to cell death or apoptosis. CsA has been reported to correct mitochondrial dysfunction and muscle apoptosis in patients with Ullrich congenital muscular dystrophy and Bethlam myopathy [(Merlini L et al. CsA corrects mitochondrial dysfunction and muscle apoptosis in patients with collagen VI myopathies. PNAS 2008; 105(13): 5225-5229]. CsA has been demonstrated in vitro to dose dependently inhibit MTP opening in isolated cardiac mitochondria, thereby preventing apoptosis and allowing the cell precious time for repair (Gomez L et al. Inhibition of mitochondrial permeability transition improves functional recovery and reduces mortality following acute myocardial infarction in mice Am J Physiol Heart Circ Physiol 2007, 293: H1654-H1661). A clinical study in 58 patients who presented with acute myocardial infarction demonstrated that administration of CsA at the time of reperfusion was associated with a smaller infarct than that seen with placebo (Piot C et al. Effect of Cyclosporine on Reperfusion Injury in Acute Myocardial Infarction. New England Journal of Medicine 2008; 395(5): 474-481)).
Chronic Neurodegenerative Diseases
CsA can act as a neuroprotective agent in cases of acute cerebral ischemia and damage as a result of head trauma (Keep M, et al. Intrathecal cyclosporine prolongs survival of late-stage ALS mice. Brain Research 2001; 894: 327-331). Animals treated with CsA showed a dramatic 80% survival rate relative to only a 10% survival rate in the absence of treatment. It was later established that this was largely the result of the binding of CsA to mitochondrial CyP-D. It has been subsequently established that the utility of CsA extends to chronic neurodegeneration, as was subsequently demonstrated in a rat model of Lou Gerhig's Disease (ALS) (U.S. Pat. No. 5,972,924), where CsA treatment more than doubled the remaining life-span. It has also recently been shown that CyP-D inactivation in CyP-D knockout mice protects axons in experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis (Forte M et al. Cyclophilin D inactivation protects axons in experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. PNAS 2007; 104(18): 7558-7563). In an Alzheimer's disease mouse model CyP-D deficiency substantially improves learning, memory and synaptic function (Du H et al. Cyclophilin D deficiency attenuates mitochondrial and neuronal perturbation and ameliorates learning and memory in Alzheimer's disease Nature Medicine 2008, 14(10): 1097-1105). In addition, CsA has been shown to be effective in a rat model of Huntington's disease (Leventhal L et al. CsA protects striatal neurons in vitro and in vivo from 3-nitropropionic acid toxicity. Journal of Comparative Neurology 2000, 425(4): 471-478), and partially effective in a mouse model of Parkinson's disease (Matsuura K et al. CsA attenuates degeneration of dopaminergic neurons induced by 6-hydroxydopamine in the mouse brain. Brain Research 1996, 733(1): 101-104). Thus, mitochondrial-dependent necrosis represents a prominent disease mechanism suggesting that inhibition of CyP-D could provide a new pharmacologic treatment strategy for these diseases (Du, 2008).
Cellular, Tissue and Organ Injury Due to a Loss of Cellular Calcium Ion (Ca2+) Homeostasis
Ca2+ is involved in a number of physiological processes at a cellular level, including healthy mitochondrial function. Under certain pathological conditions, such as myocardial infarct, stroke, acute hepatotoxicity, cholestasis, and storage/reperfusion injury of transplant organs, mitochondria lose the ability to regulate calcium levels, and excessive calcium accumulation in the mitochondrial matrix results in the opening of large pores in the inner mitochondrial membrane. (Rasola A. et al. The mitochondrial permeability transition pore and its involvement in cell death and in disease pathogenesis. Apoptosis 2007, 12: 815-833.) Nonselective conductance of ions and molecules up to 1.5 kilodaltons through the pore, a process called mitochondrial permeability transition, leads to swelling of mitochondria and other events which culminate in cell death, including the induction of apoptosis. One of the components of the MTP is CyP-D. CyP-D is an immunophilin molecule whose isomerase activity regulates opening of the MPTP, and inhibition of the isomerase activity by CsA or CsA analogs inhibits creation of the MPTP, and thus prevents cell death.
Non-Immunosuppressive Cyclosporine Analogue Cyclophilin Inhibitors
Despite the advantageous effects of CsA in the above mentioned indications, the concomitant effects of immunosuppression limit the utility of CsA as a CyP inhibitor in clinical practice. At present, there are only a few CsA analogs that have been proven to have little or reduced immunosuppressive activity (i.e., <10% of the immunosppressive potency of CsA) and still retain their ability to bind CyP (i.e., >10% CyP binding capacity as compared to CsA).
NIM 811 (Melle4-Cyclosporine)
NIM 811 is a fermentation product of the fungus Tolypocladium niveum, which is modified at amino acid 4 and displays no immunosuppressive activity (due to lack of calcineurin binding), yet retains binding affinity for CyP-A (Rosenwirth B A et al. Inhibition of human immunodeficiency virus type 1 replication by SDZ NIM 811, a nonimmunosuppressive Cyclosporine Analogue. Antimicrob Agents Chemother 1994, 38: 1763-1772).
DEBIO 025 (MeAla3EtVal4-Cyclosporin)
DEBIO 025 is a dual chemical modification of CsA at amino acids 3 and 4. DEBIO 025 also displays no immunosuppressive activity yet retains binding affinity for CyP-A PPlase activity (Kristal, 2004).
SCY-635 (DimethylaminoethylthioSar3-hydroxyLeu4-Cyclosporin)
SCY-635 is a dual chemical modification of CsA at amino acids 3 and 4. SCY-635 also displays no immunosuppressive activity yet retains binding affinity for CyP-A PPlase activity (PCT Publication No. WO2006/039668).
Generally, these compounds have modification on the face of CsA that is responsible for binding calcineurin, and generally require the modification of amino acids 3 and 4. The modification of amino acids 3 and 4 is laborious and complex, as this approach typically involves opening up the cyclosporine ring, replacing and/or modifying those amino acids and then closing up the ring to produce the modified cyclosporine.
In contrast, modification of the side chain of amino acid 1 does not require opening of the cyclosporine ring. However, amino acid 1 is associated with CyP binding (as opposed to calcineurin binding) and has been modified to increase the immunosuppressive efficacy of CsA. For example U.S. Pat. No. 6,605,593, discloses a single modification of amino acid 1 that results in a CsA analog with increased immunosuppressive potency.
Therefore, it would be desirable to have a cyclosporine analogue molecule (a “CAM”) that is readily synthesized and is efficacious in the treatment of CyP mediated diseases. It is also desirable to provide a CsA analogue that provides as least some of the functionality of native CsA, but which possesses improved or additional properties, effects or functions relative to native CsA.